A. Technical Field
The present invention relates to an insulated door for a cargo container and an insulated cargo container containing such a door. In one embodiment, the insulated door is an insulated door for a railroad boxcar.
B. Related Art
Currently, many shippers utilize insulated or refrigerated large cargo containers (such as boxcars) to transport items that require the maintenance of specified temperatures during transit. Because these containers are required to maintain certain temperatures, the thermal efficiency of these containers is an important feature. Thermal efficiency is characterized by the thermal conductivity of a particular component or its inverse, its resistance to heat transfer commonly referred to as an R value.
One area of heat loss in these containers is in the area of the door. In the past, cargo container doors were typically constructed of a combination of wood and metal members. Because members of this type typically possessed a low R-value, insulation, such as foam insulation, was often installed in these cargo container doors to increase their thermal efficiency. Even with the use of insulation, however, the thermal efficiency of cargo container doors of this type has not been as high as desired by users of these cargo containers. One reason for this lack of thermal efficiency is that it is generally impractical to make a piece of foam insulation to match the dimensions of the door. Therefore, several separate pieces of foam must be used. Typically, these foam pieces are adhered together and applied to the door. The bond lines of these pieces, however, form thermal shorts, that is, areas in the door which allow heat loss to bypass insulation, thereby causing a reduction in thermal efficiency. A method to insulate an existing door for an existing cargo container, such as a boxcar. In one implementation, the method includes attaching a liner to at least one surface of the door, incorporating an insulating layer, and attaching a gasket to the liner. A door retrofit by this method will have improved thermal efficiency. A method to insulate an existing door for an existing cargo container, such as a boxcar. In one implementation, the method includes attaching a liner to at least one surface of the door, incorporating an insulating layer, and attaching a gasket to the liner. A door retrofit by this method will have improved thermal efficiency.
In addition, current cargo container doors often include thermal shorts, at other areas of the door causing a further reduction in thermal efficiency. One common area for thermal shorts is near the edges of the door where little or no insulation is included. Therefore, there is a need for a cargo container door constructed to improve thermal efficiency and that also removes potential thermal shorts. The present invention provides a cargo container door that meets these needs.